This invention relates to polymeric pigment dispersants, more particularly, it relates to graft copolymer pigment dispersants having a urethane/urea group as the pigment anchoring group.
Polymeric pigment dispersants which are effective for dispersing pigments in organic liquids are known in the art and are used to form pigment dispersions that are used in a variety of solvent borne coating compositions. Nowadays, such pigment dispersions are widely used, for example, in pigmented exterior solvent borne paints for automobiles and trucks.
Much of the past activity with polymeric dispersants has been with random copolymers, but these relatively inefficient materials are being replaced by structured pigment dispersants such as graft copolymers. The graft copolymer dispersants that have been used in the past are described in, for example, Huybrechts U.S. Pat. No. 5,852,123 issued Dec. 22, 1998. Such graft copolymers include a polymeric backbone and macromonomer side chains grafted onto the backbone and have attached to either the macromonomer or backbone, a polar group known as a pigment anchoring group which is designed to adsorb on the surface of a pigment particle and attach the copolymer dispersant to the pigment surface.
Urea groups, as described in Huybrechts U.S. Pat. No. 5,852,123 above, are extremely powerful pigment anchoring groups. Such groups are highly insoluble in organic solvents, selectively adsorbed by a wide range of pigments, and are not easily displaced from pigment surfaces by polar solvents or other polar functional groups present in the paint system which could compete for adsorption on the pigment surfaces. Stable and non-flocculating dispersions are thus easily formed, which enables the manufacture of paints with good spray rheology and excellent color uniformity. While the past work indicates that urea containing graft copolymers are outstanding dispersants; they also suffer from certain significant drawbacks. For instance, the urea anchoring groups are customarily introduced into the graft copolymer by copolymerizing monomers containing urea functional groups into the backbone, the macromonomer, or both. However, commercially available urea functional monomers are costly and few and usually are not supplied in pure form, which leads to quality problems.
Therefore, there is still a need for new chemistries and convenient methods to broaden the choices of the types of urea groups that can be used in order to optimize the manufacture and performance of the pigment dispersants described above.